-- Discussion containing changed information from previous version are highlighted. --
493
FXUS63 KMKX 171429
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
929 AM CDT Mon Jun 17 2024

.KEY MESSAGES...

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- Hot and humid conditions expected today through Wednesday,
  with temperatures and heat index values in the 90s. The
  highest temperatures and heat index values are expected this
  afternoon.

- Isolated to scattered thunderstorms are possible this
  afternoon, with the strongest storms capable of producing
  gusty winds and small hail.

- There will be daily thunderstorm chances through the week due
  to warm and humid conditions, with the highest rain chances
  Wednesday afternoon (as a weak cold front approaches).

- Dangerous swim conditions are possible Tuesday afternoon at
  Lake Michigan beaches in Sheboygan and Ozaukee Counties.
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&&

.UPDATE...
-- Changed Discussion --
Issued 930 AM CDT Mon Jun 17 2024

Continuing to monitor the convective complex currently spanning
from eastern NE to northwestern WI as it gradually drifts
northeastward. Though this system is not expected to fully
`arrive` in our CWA, outflow boundaries ejected eastward from it
could potentially reach our northwestern CWA and serve as a
triggering mechanism for convection this afternoon. Even if said
boundaries were to miss our area completely, potential for
widely scattered thunderstorms would still be present this
afternoon (all areas), with daytime heating gradually eroding
CIN and reaching convective temps. CAMs are not in agreement on
said auto-convection, hence our PoPs for this afternoon are 20%
all areas, up to 30% for our far northern and northwestern CWA
(along and north of a Baraboo to Juneau to Sheboygan line) to
account for triggering along outflow boundaries. If convection
occurs this afternoon, it would likely be in the form of widely
scattered ordinary cells (Deep shear < 20 kts, SBCAPE over 2000
joules, DCAPE approaching 1000 joules, PW around 1.5 in), with a
threat for gusty winds and downpours. High freezing levels and
poor mid level lapse rates should prevent large hail formation.

Convection is likely to dwindle tonight with the shutdown of
daytime heating, with mostly dry weather expected. A select few
CAMs develop weak showers and thunderstorms late tonight in
response to continued southerly WAA, PoPs for this are currently
15% or less.

Sheppard
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&&

.SHORT TERM...
Issued 409 AM CDT Mon Jun 17 2024

Today through Tuesday:

Strong thermal ridging in the southeastern U.S. combined with a
deepening surface low in the lee of the Colorado Rockies will
continue to push hot, humid air into southern Wisconsin today
through Tuesday. This air mass not only will produce high heat
index values in the mid to upper 90s, but also brings chances
for thunderstorms today and Tuesday.

Temperatures will climb quickly this morning as cloud cover
remains minimal and southwesterly winds increase, reaching
highs in the 90s across much of southern Wisconsin.
Southwesterly winds and downsloping off the Kettle Moraine will
allow even areas near Lake Michigan to see temperatures in the
upper 80s to near 90 degrees.

During the afternoon hours today, isolated to scattered
thunderstorms are possible as surface temperatures rise to near
convective temperature. A well mixed boundary layer and deep WAA
combined with CAPE values over 2000 J/kg are expected to yield a
few afternoon thunderstorms, with outflows leading to additional
potential development. Bulk shear values of 20 kt or less are
expected, making organization minimal for any developing cells.
In addition, WAA aloft is expected to keep midlevel lapse rates
on the lower side and prevent large hail formation. Main concern
then turns to gusty winds within stronger storms, with DCAPE
values over 1000 J/kg and PWAT values around 1.5 inch lending
credence to precipitation loading and corresponding downburst
potential. The best chances for thunderstorm development are
from Sauk to Ozaukee County northward, as this is along the
southern side of a decaying MCS. However, the environment
remains primed across all of southern Wisconsin.

Tuesday, hot and humid conditions continue, but thunderstorm
activity looks to be more conditional. 850 mb WAA and moisture
convergence may fire a few thunderstorms across southeastern
Wisconsin during the afternoon hours, but confidence is lower
due to a lack of significant trigger. Southerly winds and cloud
cover may keep areas near Lake Michigan slightly cooler on
Tuesday.

MH

&&

.LONG TERM...
Issued 409 AM CDT Mon Jun 17 2024

Tuesday night through Sunday:

Low pressure lifts northward into Ontario by Tuesday night,
with persistent thermal ridging over the Southeast U.S. keeping
southern Wisconsin in primarily dry conditions through Tuesday
night. As surface low pressure skirts the northern edge of the
ridge into Wednesday, precipitation chances increase along a
trailing frontal feature. Thunderstorm chances remain through
the end of the week and into the weekend as a tropical
disturbance in the Gulf of Mexico feeds moisture into the
stalled boundary by way of the central Plains. Thermal ridging
in the Southeast looks to become reinforced within a region of
broad subsidence, preventing the boundary from propagating
farther south. Uncertainty remains with the exact placement of
the stalled boundary and therefore with timing and intensity of
precipitation, but general cloudiness is expected to keep
temperatures in the 80s from midweek onward.

MH

&&

.AVIATION...
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Issued 930 AM CDT Mon Jun 17 2024

Southwest winds with roughly 20 kt gusts expected this
afternoon (hence, no lake breeze expected to reach lakeshore
airports today), with south flow continuing tonight and
becoming even gustier on Tuesday (25 kt gusts).

Widely scattered showers and thunderstorms may develop this
afternoon, amounting to a roughly 20% rain chance. Cloud
coverage would increase from scattered to broken in the vicinity
of said storms, but cumulonimbus ceilings are likely to remain
VFR (generally 4000 ft or higher) with said convection. A PROB30
group for thunderstorms may be needed in the next routine TAF
issuance unless confidence decreases. Main concern would be
brief downpours with visibility restrictions, locally gusty
winds, and thunder. A patch of MVFR cigs cannot be ruled out,
but is unlikely and would require repeated hits from
thunderstorms in the same area.

Sheppard
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&&

.MARINE...
Issued 409 AM CDT Mon Jun 17 2024

Modest southerly winds will prevail through tonight. Low pressure
lifting from the northern Plains into northwestern Ontario on
Tuesday will then produce gusty southerly winds Tuesday through
Tuesday night. Small Craft Advisory conditions are possible due
to high winds and waves on Tuesday. Light southwesterly winds
are then expected as the low continues to lift into the Hudson
Bay, with a cold front slowly pushing southward across the lake
Wednesday night into Thursday, shifting winds northeasterly.

Periods of thunderstorms are expected this afternoon, with slight
chances on Tuesday morning. A few stronger thunderstorms may
produce gusty winds this afternoon. Slight chances are expected
again Tuesday afternoon across the southern half. Thunderstorms
become more likely on Wednesday into Wednesday night across the
open waters.

MH

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...None.
&&

$$

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